This invention relates to elastic laminate materials having different zones of elastic tension across a width of the material and methods for making the same.
Conventional elastic laminates for use in personal care products are composed of a continuous meltblown elastomer web or a series of identical continuous filaments bonded with a meltblown elastomer web. Such conventional stretch-bonded laminate materials exhibit homogeneous tension characteristics across the width of the laminate material. One process for producing a continuous filament stretch-bonded laminate is described in U.S. Pat. No. 5,385,775, issued to Wright, the disclosure of which is incorporated by reference. Additionally, reinforcing filaments have been produced independently of the elastomer spinning process to implement bands having greater tension.
There is a need for a targeted elastic laminate material having at least one low tension zone and at least one high tension zone, having high tension and stretch properties, not requiring separate formation of the high and low tension zones. Additionally, there is a need for a method for producing a targeted elastic laminate material that is easier and less expensive than conventional processes of making stretch-bonded laminate materials.
The present invention is directed to a targeted elastic laminate (TEL) material having a series of continuous elastomeric filaments bonded to two facing materials. The targeted elastic laminate material has at least one high tension zone having a higher basis weight, and one low tension zone having a lower basis weight, both formed from the same polymer material in the same extrusion step.
The high tension zone and low tension zone can have widths from under 0.5 inch to 50 inches or greater, depending on the processing equipment and the anticipated application. For instance, in a disposable absorbent article, such as training pants, one or more zones of high tension having a width of about 0.5-3 inches, can be produced adjacent to a low tension zone covering the remaining width of the material sheet. The high tension zone may have a tension 1 to 8 times, alternatively about 2 to 4 times, greater than the tension of the low tension zone, at 50% elongation of the fabric.
In one preferred embodiment of this invention, the TEL is made by a vertical filament stretch-bonded laminate (VF SBL) method. In another preferred embodiment, the TEL is made by a continuous filament stretch-bonded laminate (CF SBL) method, which is a modification of the process described in U.S. Pat. No. 5,385,775 to Wright. In either case, a first nonwoven web made from a single polymer or polymer blend contains a first zone of first filaments adjacent a second zone of second filaments, the first and second zones having different average basis weights. The plurality of first filaments are extruded, cooled and stretched to form at least one low tension zone and the plurality of second filaments are extruded, cooled and stretched to form at least one high tension zone. The first and second filaments may be extruded through a single die. To make a stretch-bonded TEL, the filaments are stretched (e.g., uniformly) to about 2 times to about 8 times of their initial length. While the first nonwoven web is in the stretched condition, it is laminated and bonded to at least one, and alternatively two, polymeric layers which have not been stretched. The laminate is allowed to retract, and has different tensions corresponding to the different zones.
In one embodiment of this invention, the VF SBL or CF SBL method is modified to have first and second spinning systems with first and second dies positioned laterally adjacent to each other, to produce a single web having low tension zone filaments and high tension zone filaments of the same elastomeric polymer or polymer blend. The filaments in the high tension zone have a higher basis weight accomplished through larger filaments or higher filament frequency than the filaments in the low tension zone. The second spinnerette used to form the high tension zone has larger extrusion holes, and/or higher hole frequency, than the first spinnerette used to make the low tension zone.
In another embodiment of this invention, the second spinning system is replaced with a set of individually controlled die plates positioned lateral to and/or downstream from the first die. The second spinning system allows placement of the second filaments in between and/or on top of the first filaments to increase the basis weight and tension in a desired fabric zone.